RESET (INTEGRAL) CONTROL SYSTEMS
The positive 0.5% per second indicates that the controller output increases from its initial point
of 50% at 0.5% per second. This causes the control valve to open further at a rate of 0.5% per
second, increasing flow.
Figure 21 Reset Controller Response
The controller acts to return the process to the setpoints. This is accomplished by the
repositioning of the control valve. As the controller causes the control valve to reposition, the
measured variable moves closer to the setpoint, and a new error signal is produced. The cycle
repeats itself until no error exists.
The integral controller responds to both the amplitude and the time duration of the error signal.
Some error signals that are large or exist for a long period of time can cause the final control
element to reach its "fully open" or "fully shut" position before the error is reduced to zero. If
this occurs, the final control element remains at the extreme position, and the error must be
reduced by other means in the actual operation of the process system.